In recent years, problems caused by recycling municipal solid waste (MSW) still remain a significant challenge to the global environment. Plastic wastes are the major portions among different types of waste being disposed. Conventional methods of recycling plastic wastes include landfill and incineration. However, these methods lead to serious concerns on the environment and human health, and they have drawn more public attention due to the side effects.
On the other hand, there is an increasing demand for recycling/reusing plastic wastes, due to the concern of resource consumption. Thermoplastic resins can be fluidized by heating so that they can be remolded and reused as raw materials for further production. On the contrary, thermoset wastes, which contribute to nearly half of all plastic wastes, are impossible to recycle. The most challenging point of recycling thermoset wastes is that they cannot be fluidized through conventional heating methods, due to the dense structure of their three-dimensional network. The networks exist as linkages between the macromolecule chains, which may cause decomposition of thermoset wastes before melting, at a high temperature of above 600° C.
Therefore, most thermoset wastes are directly disposed to a landfill or incinerator for recycling. However, none of the existing recycling methods are cost-effective, environmentally friendly or continuous. The existing methods, such as treating the thermoset wastes by chemical reagents under high temperature and pressure in an enclosed autoclave reactor, are proven to have low efficiency and productivity, and high consumption of power and chemicals. Therefore, it is necessary to develop a more cost-efficient and safer method for recycling thermoset plastic wastes.